Maximum Width of Binary Tree.cpp

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution 
{
public:
    int widthOfBinaryTree(TreeNode* root) 
    {
        if (!root) return 0;
        int res = 0;
        queue<pair<TreeNode*,int>> q;
        q.push({root, 1});
        while (!q.empty()) 
        {
            if (q.size() == 1) 
                q.front().second = 1;
            int left = q.front().second, right = left, n = q.size();
            for (int i = 0; i < n; ++i) 
            {
                auto t = q.front().first; 
                right = q.front().second; q.pop();
                if (t->left) 
                    q.push({t->left, right * 2});
                if (t->right) 
                    q.push({t->right, right * 2 + 1});
            }
            res = max(res, right - left + 1);
        }
        return res;
    }
};